Wireless LAN communication method and apparatus

ABSTRACT

A wireless local area network (WLAN) communication method and apparatus are provided. The WLAN communication method includes allowing a receiving station to receive a multi input multi output (MIMO) frame, allowing the receiving station to determine whether the MIMO frame is erroneous and whether the MIMO frame is destined for the receiving station, allowing the receiving station to generate a single input single output (SISO) acknowledgement (ACK) frame if the MIMO frame is not erroneous and is destined for the receiving station, and allowing the receiving station to transmit the SISO ACK frame to a sending station that has transmitted the MIMO frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No.10-2004-0070931 filed on Sep. 6, 2004 in the Korean IntellectualProperty Office, and U.S. Provisional Patent Application No. 60/601,135filed on Aug. 13, 2004 in the United States Patent and Trademark Office,the disclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present invention relate towireless local area network (LAN) communications, and more particularly,to wireless LAN (WLAN) communications using an improved carrier sensingmechanism.

2. Description of the Related Art

Recently, there is an increasing demand for ultra high-speedcommunication networks due to widespread public use of the Internet anda rapid increase in the amount of available multimedia data. Since LANsemerged in the late 1980s, the data transmission rate over the Internethas drastically increased from about 1 Mbps to about 100 Mbps. Thus,high-speed Ethernet transmission has gained popularity and wide spreaduse. Currently, intensive research into a gigabit speed Ethernet isunder way. An increasing interest in the wireless network connection andcommunication has triggered research into and development of WLANs,greatly increasing availability of WLANs to consumers. Although use ofWLANs may reduce performance in view of lower transmission rate andpoorer stability as compared to wired LANs, WLANs have variousadvantages, including wireless networking capability, greater mobilityand so on. Accordingly, WLAN markets have been gradually growing.

Due to the need for a greater transmission rate and the development ofwireless transmission technology, the initial IEEE 802.11 standard,which specifies a 1 to 2 Mbps transfer rate, has evolved into advancedstandards including 802.11b and 802.11a. Currently, a new IEEE standard,802.11g, is being discussed by the Standardization Conference groups.The IEEE 802.11g standard, which delivers a 6 to 54 Mbps transmissionrate in the 56 GHz-National Information Infrastructure (NII) band, usesorthogonal frequency division multiplexing (OFDM) as transmissiontechnology. With an increasing public interest in OFDM transmission anduse of a 5 GHz band, much greater attention is been paid to the OFDMthan other wireless standards.

Recently, wireless Internet services using WLAN, so-called “Nespot,”have been launched and offered by Korea Telecommunication (KT)Corporation of Korea. Nespot services allow access to the Internet usinga WLAN according to IEEE 802.11b, commonly called Wi-Fi representingwireless fidelity. Communication standards for wireless datacommunication systems, which have been completed and promulgated or arebeing researched and discussed, include Wide Code Division MultipleAccess (WCDMA), IEEE 802.11x, Bluetooth, IEEE 802.15.3, etc., which areknown as 3rd Generation (3G) communication standards. The most widelyknown, cheapest wireless data communication standard is IEEE 802.11b, aseries of IEEE 802.11x. An IEEE 802.11b WLAN standard delivers datatransmission at a maximum rate of 11 Mbps and utilizes the 2.4GHz-Industrial, Scientific, and Medical (ISM) band, which can be used atbelow a predetermined electric field without permission. With the recentwidespread use of the IEEE 802.11a WLAN standard, which delivers amaximum data rate of 54 Mbps in the 5 GHz band by using OFDM, IEEE802.11g developed as an extension to the IEEE 802.11a for datatransmission in the 2.4 GHz band using OFDM is intensively beingresearched.

The Ethernet and the WLAN, which are currently being widely used, bothutilize a carrier sensing multiple access (CSMA) method. According tothe CSMA method, it is determined whether a channel is in use or not inuse. If the channel is not in use, that is, if the channel is idle, thendata is transmitted. If the channel is busy, retransmission of data isattempted after a predetermined period of time. A carrier sensingmultiple access with collision detection (CSMA/CD) method, which is animprovement of the CSMA method, is used in a wired LAN, whereas acarrier sensing multiple access with collision avoidance (CSMA/CA)method is used in packet-based wireless data communications. In theCSMA/CD method, a station suspends transmitting signals if a collisionis detected during transmission. Compared with the CSMA method, in whichit is pre-checked whether a channel is occupied or not beforetransmitting data, in the CSMA/CD method, the station suspendstransmission of signals when a collision is detected during thetransmission of signals and transmits a jam signal to another station toinform it of the occurrence of the collision. After the transmission ofthe jam signal, the station has a random backoff period for delay andrestarts transmitting signals. In the CSMA/CD method, the station doesnot transmit data immediately even after the channel becomes idle andhas a random backoff period for a predetermined duration beforetransmission to avoid collision of signals. If a collision of signalsoccurs during transmission, the duration of the random backoff period isincreased by two times, thereby further lowering a probability ofcollision.

As described above, conventionally, a single input single output (SISO)approach has been adopted for WLAN communications based on a CSMA/CAmethod. That is to say, a station (hereinafter referred to as an “SISOstation”) that adopts the SISO approach receives data from and transmitsdata to a wireless medium using a single antenna. However, in recentyears, research on wireless communications based on a multiple inputmultiple output (MIMO) approach has been vigorously carried out. Astation (hereinafter referred to as an “MIMO station”) that adopts theMIMO approach, unlike an SISO station, transmits a plurality of data toa wireless medium via different transmission paths using a plurality ofantennas and receives a plurality of data from another MIMO station viadifferent transmission paths using the antennas. Accordingly, an MIMOstation achieves higher data rates (data transferring rates) than anSISO station. However, in a WLAN where an MIMO station and an SISOstation coexist, the SISO station may not be able to interpret any datatransmitted by the MIMO station. Problems that may arise in such a WLANwill now be described in detail with reference to FIGS. 1 through 3.

FIG. 1 is a diagram illustrating the format of an IEEE 802.11a frame.

Referring to FIG. 1, the IEEE 802.11a frame is comprised of a physicallayer convergence procedure (PLCP) preamble 110, a signal field 120, anda data field 130.

The PLCP preamble 110 indicates what data will be transmitted on acurrent physical layer. The signal field 120, which follows the PLCPpreamble 110, includes one orthogonal frequency-division multiplexing(OFDM) symbol that is modulated at a lowest data rate using a basicmodulation method. The data field 130 includes a plurality of OFDMsymbols that are modulated at data rates higher than or equal to thedata rate at which the OFDM symbol of the signal field 120 is modulated.

The signal field 120 is comprised of a total of 24 bits. In detail, thefirst through fourth bits of the signal field 120 constitute a ratefield 142, which specifies how and at what coding rate the data field130 has been modulated. The fifth bit of the signal field 120 is areserved bit. The sixth through seventeenth bits of the signal field 120constitute a length field 144, which specifies the length of the IEEE802.11a frame.

The eighteenth bit of the signal field 120 is a bit used for paritycheck. The nineteenth through twenty fifth bits of the signal field 120are tail bits. The length field 144 specifies the number of bytesconstituting a media access control (MAC) frame contained in the datafield 130. First through sixteenth bits of the data field 130 constitutea service field. The signal field 120 and the service field constitute aPLCP header 140. The data field 130 also includes a PLCP service dataunit (PSDU), six tail bits, and pad bits. The PSDU corresponds to an MACframe, which is comprised of an MAC header, an MAC data field, and aframe check sequence (FCS) used for determining whether the MAC frame iserroneous. The data field 130 may be modulated in various manners and atvarious coding rates. As described above, information regarding how andat what coding rate the data field 130 has been modulated is included inthe rate field 142 of the signal field 120.

FIG. 2 is a diagram illustrating a carrier sensing operation performedin a WLAN.

Two carrier sensing methods, i.e., a physical carrier sensing method anda virtual carrier sensing method, are currently available for WLANcommunications. The physical carrier sensing method and the virtualcarrier sensing method will now be described in detail with reference tothe accompanying drawings. Referring to FIG. 2, a frame 212, which isreceived by a physical layer 210, is comprised of a PLCP preamble 214, asignal field 216, and a data field 218.

The physical carrier sensing method enables a station to recognizewhether signals are transmitted by a wireless medium. In other words,when the PLCP preamble 214 is input to the physical layer 210, thephysical layer 210 notifies an MAC layer 220 that it is currently usedby transmitting a busy signal to the MAC layer 220, as marked by 222.Thereafter, when the reception of the PLCP preamble 214 is completed,the physical layer 210 notifies the MAC layer 220 that it is idle bytransmitting an idle signal 228 to the MAC layer 220.

A physical carrier sensing operation may be performed based on a resultof interpreting a length field included in the signal field 216. Thevirtual carrier sensing method is a method that enables the MAC layer220 to determine whether a wireless medium is used based on a result ofinterpreting a duration value, i.e., a network allocation vector (NAV)value, contained in an MAC frame included in the data field 218.Therefore, for a predetermined period of time specified by the durationvalue, the MAC layer 220 considers that the wireless medium is used. Astation can receive the data field 218 and then read the NAV value fromthe MAC frame included in the received data field 218.

FIG. 3 is a diagram illustrating a conventional method of transmittingframes in a contention period in a WLAN where three MIMO stations, i.e.,first through third MIMO stations, and an SISO station coexist.

According to the physical carrier sensing method, stations are preventedfrom transmitting frames via a wireless channel when frames aretransmitted via the wireless channel by other stations. In a contentionmode, stations cannot transmit a next frame immediately after thewireless channel becomes empty but are required to wait for apredetermined amount of time called a distributed inter-frame space(DIFS) and random back-off time to obtain the opportunity to transmit aframe via the wireless channel.

Referring to FIG. 3, the first MIMO station obtains the opportunity totransmit data through channel contention and thus transmits a data frameto the second MIMO station. Since the data frame transmitted by thefirst MIMO station is an MIMO frame, the third MIMO station as well asthe second MIMO station can receive it, but the SISO station cannotreceive it. Following a short inter-frame space (SIFS) after receivingthe data frame transmitted by the first MIMO station, the second MIMOstation transmits an acknowledgement (ACK) frame to the first MIMOframe.

Since the SIFS is shorter than the DIFS and the second MIMO stationtransmits the ACK frame following a short period of time after receivingthe data frame transmitted by the first MIMO station, the second andthird MIMO stations and the SISO station cannot transmit data until thetransmission of the ACK frame is completed. Since the ACK frame is alsoan MIMO frame, the third MIMO station as well as the first MIMO stationcan receive it, but the SISO station cannot receive it.

The first through third MIMO stations can set their respective NAVvalues based on MIMO data that they receive by performing a virtualcarrier sensing operation. Accordingly, the first through third MIMOstations can obtain the opportunity to transmit a next frame the DIFSand back-off time 310 after the transmission of the ACK frame iscompleted.

However, the SISO station cannot receive the MIMO data and thus cannotperform a virtual carrier sensing operation. In other words, while notreceiving any data frame, the SISO frame considers that a collisionbetween data frames has occurred. Therefore, the SISO station can obtainthe opportunity to transmit a frame following an extended inter-framespace (EIFS) and back-off time 320 after performing a physical carriersensing operation, and the EIFS is equal to the sum of the SIFS and apredetermined amount of time required for transmitting an ACK frame at alowest data rate. In other words, the SISO station must wait a longperiod of time to obtain the opportunity to transmit a frame in anenvironment where it exists together with the first through third MIMOstations. Thus, the SISO station is in a disadvantageous position inchannel contention with the first through third MIMO stations or othernew MIMO stations. Therefore, it is necessary to develop a WLANcommunication method that can prevent SISO stations from beingdiscriminated against MIMO stations in an environment where they existtogether with the MIMO stations.

SUMMARY OF THE INVENTION

The present invention provides a WLAN communication method and apparatususing an improved carrier sensing method.

According to an aspect of the present invention, there is provided aWLAN communication method including allowing a receiving station toreceive a MIMO frame, allowing the receiving station to determinewhether the MIMO frame is erroneous and whether the MIMO frame isdestined for the receiving station, allowing the receiving station togenerate SISO ACK frame if the MIMO frame is not erroneous and isdestined for the receiving station, and allowing the receiving stationto transmit the SISO ACK frame to a sending station that has transmittedthe MIMO frame.

According to another aspect of the present invention, there is provideda WLAN communication method including allowing a sending station togenerate an MIMO frame, allowing the sending station to transmit theMIMO frame to a receiving station, and allowing the sending station toreceive an SISO ACK frame transmitted by the receiving station inresponse to the MIMO frame.

According to still another aspect of the present invention, there isprovided a wireless LAN communication method including allowing asending station to determine how an MAC frame is to be transmitted,allowing the sending station to generate an MIMO frame based on the MACframe if the sending station decides to transmit the MAC frame in anMIMO approach, and allowing the sending station to generate an SISOframe based on the MAC frame if the sending station decides to transmitthe MAC frame in an SISO approach, and allowing the sending station totransmit the generated MIMO or SISO frame in the selected approach.

According to a further aspect of the present invention, there isprovided a station including a physical layer, which receives an MIMOframe transmitted via a wireless medium and obtains an MAC frame fromthe received MIMO frame, and an MAC layer, which determines whether theMAC frame is erroneous and whether the MAC frame is destined for thestation, and generates an ACK frame and then provides the generated ACKframe to the physical layer if the MAC frame is not erroneous and isdestined for the station, wherein the physical layer generates an SISOACK frame based on the ACK frame provided by the MAC layer and providesthe generated SISO ACK frame to the wireless medium.

According to a yet another aspect of the present invention, there isprovided a station including an MAC layer, which generates an MAC frameand determines how the generated MAC frame is to be transmitted, and aphysical layer, which generates an MIMO frame or an SISO frame based onthe MAC frame based on the determination results and transmits thegenerated MIMO or SISO frame to a wireless medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a diagram illustrating the format of an IEEE 802.11a frame;

FIG. 2 is a diagram illustrating conventional carrier sensing methodsfor wireless communications;

FIG. 3 is a diagram illustrating a conventional method of transmittingframes in a contention period in a conventional WLAN where MIMO stationsand an SISO station coexist;

FIG. 4 is a diagram illustrating the formats of a data frame and an ACKframe according to an exemplary embodiment of the present invention;

FIG. 5 is a diagram illustrating a method of transmitting frames in acontention period in a wireless LAN where MIMO stations and an SISOstation coexist;

FIG. 6 is a flowchart illustrating the operation of a sending stationaccording to an exemplary embodiment of the present invention;

FIG. 7 is a flowchart illustrating the operation of a receiving stationaccording to an exemplary embodiment of the present invention;

FIG. 8 is a flowchart illustrating a carrier sensing method performed byan SISO station according to an exemplary embodiment of the presentinvention;

FIG. 9 is a block diagram of an MIMO station according to an exemplaryembodiment of the present invention; and

FIG. 10 is a block diagram of an MIMO station according to anotherexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. It is assumed in this disclosure that an MIMOstation has two input ports and two output ports. However, the presentinvention is also applicable to an MIMO station having more than twoinput ports and more than two output ports and to an SIMO station havinga single input port and multiple output ports and an MISO station havingmultiple input ports and a single output port.

FIG. 4 is a diagram illustrating the formats of a data frame and an ACKframe according to an exemplary embodiment of the present invention.

In the present exemplary embodiment, an MIMO data frame is used tofacilitate a physical carrier sensing operation, and an SISO ACK frameis used to facilitate a virtual carrier sensing operation even when theMIMO data frame is received.

The structure of a data frame will now be described in detail withreference to FIG. 4.

Referring to FIG. 4, a data frame includes a first PLCP preamble 410, asignal field 420, a second PLCP preamble 450, and a data field 430. Thedata frame may optionally include a supplementary signal field 460. OFDMsymbols received by antenna 1 of a receiving station and OFDM symbolsreceived by antenna 2 of the receiving station coexist in the data field430.

The first PLCP preamble 410 is a signal that antenna 1 is to synchronizeitself with, and the second PLCP preamble 450 is a signal that antenna 2is to synchronize itself with. In the present exemplary embodiment, thesignal field 420 follows the first PLCP preamble 410. The first PLCPpreamble 410 and the signal field 420 have the same structures as thefirst PLCP preamble 110 and the signal field 120, respectively, ofFIG. 1. Thus, even an SISO station can obtain information contained inthe signal field 420, for example, information regarding data rateinformation and frame length. The frame length indicates the length inbytes of part of the data frame following the signal field 420, i.e.,the sum of the lengths in bytes of the second PLCP preamble 450, thesupplementary signal field 460, and the data field 430. In other words,a station can obtain the duration of the fields following the signalfield 460 by dividing the frame length by the data rate.

For example, if the data rate is 108 Mbps (54 Mbps per antenna), theduration of the second PLCP preamble 450 is 8 microseconds, thesupplementary signal field 460 is 0 bytes, and the data field 430contains n-byte data, then the frame length is calculated in thefollowing manner. The duration of each OFDM symbol is four microseconds,and the second PLCP preamble 450 corresponds to two OFDM symbols. Since216×2 byte-data per OFDM symbol can be transmitted at a data rate of 108Mbps, it appears that the second PLCP preamble 450 has a length of 432bytes. Therefore, n+432 is recorded as the frame length in a lengthfield of the data frame.

If the data rate is 12 Mbps (6 Mbps per antenna), the duration of thesecond PLCP preamble 450 is 8 microseconds, the supplementary signalfield 460 is comprised of 0 bytes, the data field 430 contains n-bytedata, then the frame length is calculated in the following manner. Asdescribed above, the duration of each OFDM symbol is four microseconds,and the second PLCP preamble 450 corresponds to two OFDM symbols. Since24×2 byte-data per OFDM symbol can be transmitted at a data rate of 108Mbps, it appears that the second PLCP preamble 450 is has a length of 48bytes. Therefore, n+48 is recorded as the frame length in a length fieldof the data frame.

In the present exemplary embodiment, an SISO frame still cannot receivean MIMO frame but can obtain information regarding the data rate and thelength of the MIMO frame. Accordingly, an SISO station can perform aphysical carrier sensing operation with reference to the frame lengthinformation as well as a power level. Therefore, according to thepresent invention, a station can more efficiently carry out a clearchannel assessment (CCA) mechanism.

The structure of an ACK frame will now be described with reference toFIG. 4. The IEEE 802.11 standard prescribes that an ACK frame or aclear-to-send (CTS) frame must be transmitted at the same data rate as aframe that it follows as a response frame. Therefore, if a stationreceives an MIMO frame, it must transmit an MIMO ACK frame in responseto the received MIMO frame, in which case, an SISO station cannotreceive the MIMO ACK frame. Thus, in the present exemplary embodiment, astation is required to transmit an SISO ACK frame in response to a frameinput thereto even though the input frame is an MIMO frame.

Referring to FIG. 4, an ACK frame includes a PLCP preamble 412 and asignal field 422. A block ACK frame based on the IEEE 802.11e standardmay also include a data field 432.

The operation of a WLAN in a case where a station transmits an SISO ACKframe in response to a frame input thereto regardless of the type of theinput frame will now be described in detail with reference to FIG. 5.

FIG. 5 illustrates a total of four stations, i.e., first through thirdMIMO stations (MIMO stations 1 through 3) and an SISO station (SISOstation).

Referring to FIG. 5, the first MIMO station obtains the opportunity totransmit data through channel contention and thus transmits a data frameto the second MIMO station. Since the data frame transmitted by thefirst MIMO station is an MIMO frame, the third MIMO station can receiveit, but the SISO station cannot receive it. However, in the presentexemplary embodiment, unlike in the prior art, the SISO station canobtain information regarding data rate and frame length from a signalfield of the data frame transmitted by the first MIMO station, and thuscan efficiently perform a physical carrier sensing operation based onthe information regarding data rate and frame length.

Following a short inter-frame space (SIFS) after receiving the dataframe transmitted by the first MIMO station, the second MIMO stationtransmits an ACK frame to the first MIMO station in response to thereceived data frame. In the present exemplary embodiment, unlike in theprior art, the ACK frame transmitted by the second MIMO station is anSISO ACK frame. Thus, the SISO station as well as the first and thirdMIMO stations can receive the ACK frame transmitted by the second MIMOstation. The third MIMO station obtains an MAC frame from the data frametransmitted by the first MIMO station and sets its NAV value 520 byperforming a virtual carrier sensing operation. The SISO station obtainsan MAC frame from the ACK frame transmitted by the second MIMO stationand sets its NAV value 530 by performing a virtual carrier sensingoperation.

Accordingly, following a DIFS and back-off time 510 after transmittingor receiving the ACK frame, the first through third MIMO stations andthe SISO station may have the opportunity to transmit a frame.

The operations of a sending station and a receiving station and acarrier sensing operation will now be described in detail.

FIG. 6 is a flowchart illustrating the operation of a sending stationaccording to an exemplary embodiment of the present invention.

Referring to FIG. 6, in operation S610, an MAC layer of the sendingstation receives data from an upper layer. In operation S620, the MAClayer of the sending station generates an MAC frame by attaching an MACheader and a frame check sequence (FCS) to the received data.

In operation S630, a physical layer of the sending station receives theMAC frame and generates a data frame by attaching two PLCP preambles tothe received MAC frame. In operation S640, the sending station transmitsthe data frame to a wireless medium.

In operation S650, the sending station determines whether it hasreceived an ACK frame within a predetermined amount of time. If thesending station has received an ACK frame, the entire process oftransmitting the data frame is completed. However, if the sendingstation has not received an ACK frame, it determines that thetransmitting of the data frame in operation S640 was erroneous.

Therefore, in operation S660, the sending station doubles the size of aback-off contention window, contends with other stations, andretransmits the data frame to the wireless medium.

In operation S650, the sending station determines again whether it hasreceived an ACK frame within the predetermined amount of time. If thesending station has received an ACK frame within the predeterminedamount of time, the entire process of transmitting the data frame iscompleted.

FIG. 7 is a flowchart illustrating the operation of a receiving stationaccording to an exemplary embodiment of the present invention.

Referring to FIG. 7, in operation S710, the receiving station detects afirst PLCP preamble and then recognizes that a data frame (hereinafterreferred to as a “current data frame”) is currently input thereto.

In operation S720, if a first antenna of the receiving station issynchronized with the detected first PLCP preamble, the receivingstation receives a signal field which contains information regarding adata rate and a frame length.

In operation S730, the receiving station determines whether the currentdata frame is an MIMO frame. In operation S740, if the current dataframe is an MIMO frame, the receiving station detects a second PLCPpreamble, and then a second antenna of the receiving station issynchronized with the detected PLCP preamble. Otherwise, however, thedetecting of the second PLCP preamble is skipped.

In operation S750, once the receiving station is synchronized with thecurrent data frame using the first and/or second preambles, it extractsan MAC frame from a data field of the current data frame. In operationS760, the receiving station determines whether the current data frame iserroneous with reference to an FCS of the extracted MAC frame andwhether the current data frame is destined for it with reference to anMAC header of the extracted MAC frame.

In operation S770, if the current data frame is not erroneous and isdestined for the receiving station, the receiving station generates anACK frame having one PLCP preamble in response to the current dataframe. In operation S780, the receiving station transmits the ACK frameto a wireless medium.

However, if the current data frame is erroneous and is not destined forthe receiving station, the receiving station abandons the current dataframe in operation S790.

FIG. 8 is a flowchart illustrating a carrier sensing operation performedby an SISO station according to an exemplary embodiment of the presentinvention.

Referring to FIG. 8, in operation S810, when a data frame is receivedvia a wireless medium, an SISO station detects a first PLCP preamble. Inoperation S820, the SISO station receives a signal field. In operationS830, the SISO station obtains information regarding data rate and framelength by interpreting the received signal field and then performs aphysical carrier sensing operation based on the obtained information.However, the SISO station cannot obtain an MAC frame yet and thus cannotset its NAV value yet by performing a virtual carrier sensing operation.

In operation S840, the SISO station receives an ACK frame. In thepresent exemplary embodiment, the ACK frame received by the SISO stationis an SISO ACK frame, and thus, even the SISO station can receive it.Accordingly, in operation S850, the SISO station extracts an MAC framefrom the received ACK frame. In operation S880, the SISO station obtainsinformation necessary for setting its NAV value from a duration field ofan MAC header and sets its NAV value based on the obtained information.

FIG. 9 is a block diagram of an MIMO station according to an exemplaryembodiment of the present invention.

Referring to FIG. 9, the MIMO station includes a physical layer 910, anMAC layer 920, and an upper layer 930.

The physical layer 910 includes an SISO PLCP module 912, an MIMO PLCPmodule 916, an MIMO codec 914, and a wireless transmission/receptionmodule 918.

In a process of transmitting a data frame, the SISO PLCP module 912,like a conventional SISO PLCP module, receives an MAC frame from the MAClayer 920 and generates an SISO frame by attaching a PLCP preamble andadditional information to the received MAC frame. In a process ofreceiving a data frame, the SISO PLCP module 912 obtains an MAC frame byremoving a PLCP header from an SISO frame received by the wirelesstransmission/reception module 918 and then transmits the obtained MACframe to the MAC layer 920.

In the process of transmitting a data frame, the MIMO PLCP module 916obtains MIMO data by coding an MAC frame with the use of the MIMO codec914 and then generates an MIMO frame by attaching first and second PLCPpreambles and additional information to the obtained MIMO data. In theprocess of receiving a data frame, the MIMO PLCP module 916 obtains MIMOdata by removing a PLCP header from an MIMO frame received by thewireless transmission/reception module 918 and then provides theobtained MIMO data to the MIMO codec 914.

In the process of transmitting a data frame, the MIMO codec 914 obtainsMIMO data by coding an MAC frame received from the MAC layer 920 andprovides the obtained MIMO data to the MIMO PLCP module 916. In theprocess of receiving a data frame, the MIMO codec 914 receives MIMO datafrom the MIMO PLCP module 916 and provides the received MIMO data to theMAC layer 920.

In the process of transmitting a data frame, the wirelesstransmission/reception module 918 receives an SISO frame or an MIMOframe and transmits the received SISO or MIMO frame to a wireless medium(not shown). In the process of receiving a data frame, the wirelesstransmission/reception module 918 receives an SISO frame or an MIMOframe and transmits the received SISO or MIMO frame to the SISO PLCPmodule 912 or the MIMO PLCP module 916.

The MAC layer 920 includes an MAC frame generation module 924, an MACframe interpretation module 926, and an ACK frame generation module 922.

In the process of transmitting a data frame, the MAC frame generationmodule 924 generates an MAC frame by attaching an MAC header and an FCSto data received from the upper layer 930 and transmits the generatedMAC frame to the physical layer 910. In a case where the MIMO stationtransmits an MIMO frame, the MAC frame generated by the MAC framegeneration module 924 is transmitted to the MIMO codec 914. On the otherhand, in a case where the MIMO station transmits an SISO frame, the MACframe generated by the MAC frame generation module 924 is transmitted tothe SISO PLCP module 912.

In the process of receiving a data frame, the MAC frame interpretationmodule 926 receives an MAC frame from the physical layer 910 anddetermines whether the received MAC frame is erroneous with reference toan FCS of the received MAC frame. If the received MAC frame iserroneous, the MAC frame interpretation module 926 abandons the receivedMAC frame. However, if the received MAC frame is not erroneous, the MACframe interpretation module 926 determines whether the received MACframe is destined for the MIMO station with reference to a header of thereceived MAC frame. If the received MAC frame is destined for the MIMOstation, the MAC frame interpretation module 926 transmits an MAC frameMSDU from which the MAC header and the FCS are removed to the upperlayer 930. However, if the received MAC frame is not destined for theMIMO station, the MAC frame interpretation module 926 abandons thereceived MAC frame.

The ACK frame generation module 922 generates an ACK frame if thereceived MAC frame is not erroneous and is destined for the MIMOstation. Thereafter, the ACK frame generation module 922 transmits thegenerated ACK frame to the SISO PLCP module 912.

FIG. 10 is a block diagram of an MIMO station according to anotherexemplary embodiment of the present invention.

Referring to FIG. 10, the MIMO station includes a physical layer 1010,an MAC layer 1020, and an upper layer 1030. The physical layer 1010includes an SISO PLCP module 1012, an MIMO PLCP module 1016, an MIMOcodec 1014, and a wireless transmission/reception module 1018. Theoperations of the SISO PLCP module 1012, the MIMO PLCP module 1016, theMIMO codec 1014, and the wireless transmission/reception module 1018 arethe same as the operations of the SISO PLCP module 912, the MIMO PLCPmodule 916, the MIMO codec 914, and the wireless transmission/receptionmodule 918 of FIG. 9.

The MAC layer 1020 includes an MAC frame generation module 1024, an MACframe interpretation module 1026, an ACK frame generation module 1022,and a selection module 1028. The operations of the MAC frame generationmodule 1024, the MAC frame interpretation module 1026, and the ACK framegeneration module 1022 are the same as the operations of the MAC framegeneration module 924, the MAC frame interpretation module 926, and theACK frame generation module 922 of FIG. 9.

The selection module 1028 decides whether an MAC frame generated by theMAC frame generation module 1024 is to be transmitted in an MIMOapproach or in an SISO approach. If the MAC frame is long, the MIMOapproach is more efficient than the SISO approach. On the other hand, ifthe MAC frame is short, the SISO approach is more efficient than theMIMO approach because the MIMO approach achieves two times higher datarates than the SISO approach but incurs more overhead, such as PLCPpreambles, than the SISO approach. The selection module 1028 decides totransmit a frame to be broadcasted or multicasted, or a control frame ora management frame in the SISO approach because the frame to bebroadcasted or multicasted must be received by a plurality of stationsand the control frame or the management frame is generally moreimportant than other frames.

If the selection module 1028 decides to transmit the MAC frame in theMIMO approach, it transmits the MAC frame to the MIMO codec 1014. On theother hand, if the selection module 1028 decides to transmit the MACframe in the SISO approach, it transmits the MAC frame to the SISO PLCPmodule 1012.

The term “module”, as used herein, means, but is not limited to, asoftware or hardware component, such as a Field Programmable Gate Array(FPGA) or Application Specific Integrated Circuit (ASIC), which performscertain tasks. A module may advantageously be configured to reside onthe addressable storage medium and configured to execute on one or moreprocessors. Thus, a module may include, by way of example, components,such as software components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. The functionality provided for in the components andmodules may be combined into fewer components and modules or furtherseparated into additional components and modules. In addition, thecomponents and modules may be implemented such that they are executedone or more computers in a communication system.

As described above, since the WLAN communication method and apparatusaccording to the present invention use an SISO ACK frame, SISO stationsare not discriminated against MIMO stations in a WLAN where the SISOstations and the MIMO stations coexist. In addition, since a signalfield is interposed between two PLCP preambles of an MIMO frame, eventhe SISO stations can obtain information necessary for performing aphysical carrier sensing operation from the signal field of the MIMOframe.

In concluding the detailed description, those skilled in the art willappreciate that many variations and modifications can be made to theexemplary embodiments without substantially departing from theprinciples of the present invention. Therefore, the disclosed exemplaryembodiments of the invention are used in a generic and descriptive senseonly and not for purposes of limitation.

1. A wireless local area network (WLAN) communication method comprising:receiving a multi input multi output (MIMO) frame at a receivingstation; determining at the receiving station whether the MIMO frame iserroneous and whether the MIMO frame is destined for the receivingstation; generating at the receiving station a single input singleoutput (SISO) acknowledgement (ACK) frame if it is determined that theMIMO frame is not erroneous and is destined for the receiving station;and transmitting the SISO ACK frame from the receiving station to asending station that has transmitted the MIMO frame.
 2. The WLANcommunication method of claim 1, wherein the MIMO frame comprises aplurality of physical layer convergence procedure (PLCP) preambles, asignal field and a data field, and the signal field follows a first PLCPpreamble of the PLCP preambles.
 3. The WLAN communication method ofclaim 2, wherein the data field contains information regarding a lengthin bytes of part of the MIMO frame following the signal field.
 4. Awireless local area network (WLAN) communication method comprising:generating at a sending station a multi input multi output (MIMO) frame;transmitting the MIMO frame from the sending station to a receivingstation; and receiving at the sending station a single input singleoutput (SISO) acknowledgement (ACK) frame transmitted by the receivingstation in response to the MIMO frame.
 5. The WLAN communication methodof claim 4, wherein the MIMO frame comprises a plurality of physicallayer convergence procedure (PLCP) preambles, a signal field, and a datafield, and the signal field follows a first PLCP preamble of the PLCPpreambles.
 6. The WLAN communication method of claim 5, wherein the datafield contains information regarding a length in bytes of part of theMIMO frame following the signal field.
 7. A wireless local area network(WLAN) communication method comprising: determining at a sending stationwhether a media access control (MAC) frame is to be transmitted in amulti input multi output (MIMO) approach or in a single input singleoutput (SISO) approach; generating at the sending station an MIMO framebased on the MAC frame if the sending station determines that the MACframe is to be transmitted in the MIMO approach, and generating at thesending station an SISO frame based on the MAC frame if the sendingstation determines that the MAC frame is to be transmitted in the SISOapproach; and transmitting from the sending station the MIMO frame inthe MIMO approach or SISO frame in the MIMO approach.
 8. The WLANcommunication method of claim 7, wherein the sending station determineswhether the MAC frame is to be transmitted in the MIMO approach or inthe SISO approach with reference to a length of the MAC frame.
 9. TheWLAN communication method of claim 7, wherein the sending stationdetermines that the MAC frame is to be transmitted in the SISO approachif the MAC frame is to be broadcasted or multicasted.
 10. The WLANcommunication method of claim 7, wherein the sending station determinesthat the MAC frame is to be transmitted in the SISO approach if the MACframe is a management frame or a control frame.
 11. A stationcomprising: a physical layer which receives a multi input multi output(MIMO) frame transmitted via a wireless medium and obtains a mediaaccess control (MAC) frame from the MIMO frame; and an MAC layer whichdetermines whether the MAC frame is erroneous and whether the MAC frameis destined for the station, generates an acknowledgement (ACK) frame,and provides the ACK frame to the physical layer if the MAC frame is noterroneous and is destined for the station, wherein the physical layergenerates a single input single output (SISO) ACK frame based on the ACKframe provided by the MAC layer, and provides the SISO ACK frame to thewireless medium.
 12. A station comprising: a media access control (MAC)layer which generates an MAC frame and determines how the MAC frame isto be transmitted; and a physical layer, which generates a multi inputmulti output (MIMO) frame or a single input single output (SISO) framebased on the MAC frame and how the MAC frame is determined to betransmitted, and transmits the MIMO frame or the SISO frame to awireless medium.
 13. The station of claim 12, wherein the MAC layerdetermines how the MAC frame is to be transmitted with reference to alength of the MAC frame.
 14. The station of claim 12, wherein the MAClayer determines that the MAC frame is to be transmitted in an SISOapproach if the MAC frame is to be broadcasted or multicasted.
 15. Thestation of claim 12, wherein the MAC layer determines that the MAC frameis to be transmitted in an MIMO approach if the MAC frame is amanagement frame or a control frame.
 16. A computer-readable recordingmedium storing a computer program for executing a wireless local areanetwork (LAN) communication method, the WLAN communication methodcomprising: receiving a multi input multi output (MIMO) frame at areceiving station; determining at the receiving station whether the MIMOframe is erroneous and whether the MIMO frame is destined for thereceiving station; generating at the receiving station a single inputsingle output (SISO) acknowledgement (ACK) frame if it is determinedthat the MIMO frame is not erroneous and is destined for the receivingstation; and transmitting the SISO ACK frame from the receiving stationto a sending station that has transmitted the MIMO frame.
 17. Acomputer-readable recording medium storing a computer program forexecuting a wireless local area network (WLAN) communication method, theWLAN communication method comprising: generating a multi input multioutput (MIMO) frame at a sending station; transmitting the MIMO framefrom the sending station to a receiving station; and receiving at thesending station a single input single output (SISO) acknowledgement(ACK) frame transmitted by the receiving station in response to the MIMOframe.
 18. A computer-readable recording medium storing a computerprogram for executing a wireless local area network (WLAN) communicationmethod, the WLAN communication method comprising: determining at asending station whether a media access control (MAC) frame is to betransmitted in a multi input multi output (MIMO) approach or in a singleinput single output (SISO) approach; generating at the sending stationan MIMO frame based on the MAC frame if the sending station determinesthat the MAC frame is to be transmitted in the MIMO approach, andgenerating at the sending station an SISO frame based on the MAC frameif the sending station determines that the MAC frame is to betransmitted in an SISO approach; and transmitting from the sendingstation the MIMO frame in the MIMO approach or the SISO frame in theSISO approach.